1. Field of the Invention
This invention relates generally to the field of servoactuators, and, more particularly, to improved energy-conserving servoactuators and several improved valves therefor.
2. Description of the Prior Art
Many types of servovalves have, of course, been developed heretofore. These servovalves have typically a spool slidably mounted within the bore of a body for controlling the flow of fluid between supply and return openings and one or more control openings. An electro-mechanical driver, such as a torque motor, was operatively arranged to move the spool relative to the body for creating a desired pressure at a control opening, or for creating a desired differential pressure between two control openings. The magnitude of such spool displacement was proportional to an error signal, which was the algebraic sum of a command signal (reflecting the desired spool position) and a negative feedback signal (reflecting the actual spool position). The polarity of the error signal determined the direction of spool movement relative to the associated body.
Such a servovalve was typically associated with a conventional doubleacting fluid-powered cylinder. The servovalve was used to control the flow of fluid to and from the opposing actuator chambers.
If it was desired to move the actuator rod against an "opposing" load, the servovalve was operated such that fluid could flow from the fluid source to the expanding actuator chamber, and could flow from the contracting actuator chamber to return.
However, if the actuator rod was moved in the same direction as an "aiding" load, the pressure in the actuator contracting chamber would be greater than the pressure in the actuator expanding chamber. The conventional servovalve controlled the position of the actuator rod by metering the flow of fluid from the contracting chamber. At the same time, however, fresh fluid from the source was admitted to the expanding chamber. This arrangement was inefficient because such fresh pressurized fluid did no useful work in controlling displacement of the actuator rod when the applied load was "aiding".
In many applications, it is sometimes desired to move an actuator rod in the same direction as an "aiding" load. For example, if a servomechanism is used to move an airfoil surface, the load on the actuator rod may be "opposing" if it is desired to move the load in one direction, but "aiding" if it is desired to move the load in the opposite direction. Similarly, in an active vehicle suspension system, the load may be "opposing" on a bound stroke, but "aiding" on a rebound stroke, or vice versa.